HANOI, Vietnam (AP) — The number of international adoptions has fallen to its lowest point in 15 years, a steep decline attributed largely to crackdowns against baby-selling, a sputtering world economy and efforts by countries to place more children with domestic families.

Globally, the number of orphans being adopted by foreign parents dropped from a high of 45,000 in 2004 to an estimated 25,000 last year, according to annual statistics compiled by Peter Selman, an expert on international adoptions at Britain’s Newcastle University.

Some adoption advocates argue the decrease is also linked to a set of strict international guidelines known as the Hague Adoption Convention. Devised to ensure transparency and child protection following a rash of baby-selling and kidnapping scandals, critics say the guidelines have also been used by leading adopting nations, including the U.S., as a pretext for freezing adoptions from some countries that are out of compliance.

“It should have been a real step forward, but it’s been used in a way that’s made it a force for shutting down” adoptions in some countries, says Elizabeth Bartholet, a Harvard law professor who promotes international adoptions. “That affects thousands of children every year.”

She says places where international adoptions are stopped may ultimately see more children stuck in orphanages or on the street where they could fall prey to sex traffickers.

U.S. adoption officials and international agencies such as UNICEF say the Hague rules, which require countries to set up a central adoption authority and a system of checks and balances, are necessary to safeguard orphans and keep profit-driven players from corrupting a system that should be purely about helping children.

Alison Dilworth, adoptions division chief at the U.S. Office of Children’s Issues and a strong supporter of the Hague guidelines, says they shield adoptive parents from everyone’s worst nightmare: “God forbid, that knock on the door ... saying your child that you have raised and loved and is fully integrated into your family was stolen from a birth parent who is desperately trying to look for them.”

Much has changed from a decade ago, when busloads of would-be foreign adoptive parents flocked to orphanages in poor countries such as China, Vietnam and Guatemala to take babies home following a relatively quick and easy process.

Waits have become longer and requirements stiffer, with some countries now refusing obese or single adoptive parents and requiring proof of a certain amount of cash in the bank. Countries embroiled in scandals have pulled the plug on their programs, or been cut off by the U.S. and other countries, leaving hundreds of children in bureaucratic limbo.

Sharon Brooks, 56, of New York, knows the story all too well. She waited three and a half years for the release of a little girl in Vietnam after the U.S. froze adoptions there in 2008 amid serious fraud concerns. In January, Brooks learned the child she had named Akira-Li would instead be adopted by a Vietnamese family.

“That was my one shot,” says Brooks, who now believes she is too old to qualify for most international adoptions. “Everything in my life has been at a standstill.”

Vietnam joined the Hague convention on Feb. 1, and U.S. officials say they are hopeful adoptions will resume within the next year.

Shutdowns in countries such as Guatemala, Nepal and Kyrgyzstan have coincided with efforts to promote domestic adoptions in countries like Russia and China, where foreigners now face tightened restrictions.

China, for instance, stopped allowing single women to adopt. In the late 1990s, a third of U.S. adoptive parents fell into this category, Selman says. Advances in fertility treatments and the growing number of couples turning to surrogacy have also contributed to the global drop.

The U.S., which historically has received about half of the world’s annual international adoptions, saw a decline of more than 60 percent from 2004 to just over 9,000 last year.

Dilworth, the U.S. adoption official, says the economic downturn is at least partly to blame, with foreign adoptions typically costing between $20,000 to $40,000.

But the U.S. freeze on adoptions from some countries also means there are fewer children available to adopt.

Guatemala used to provide up to 4,000 children a year for international adoption at its peak in 2006. But the U.S. will not accept further adoptions from the country until it has fully revamped its system to root out corruption, Dilworth says.

“They have incredible problems with fraud,” she says.

In one recent high-profile case, a Guatemalan court ruled that an American family must return their 7-year-old adopted daughter to her birth mother after allegations surfaced that the girl was snatched from her home five years ago. The child remains in the U.S.

Other countries that have seen large drops in the adoption of foreign babies include Spain and France, where international adoption fell 48 percent and 14 percent respectively from 2004 to 2010. Canada remained the same and Italy actually saw a 21 percent increase during that period, according to Selman, who analyzed data from 23 countries that are primary receivers of adopted orphans.

Last year’s 25,000 international adoptions were the lowest since 1996, Selman said.

The global numbers could decline further as South Korea, one of the top providers of orphans for foreign adoption, works to phase out its long-running program.

Since the 1950s, more than 170,000 South Korean children were adopted by families overseas, with the majority going to the United States. Despite having one of the world’s fast-growing economies and domestic concern about falling birth rates that are already among the world’s lowest, South Korea continues to rank as a top destination for international adoption. Experts blame this on a strong cultural stigma against both unwed motherhood and adoption.

But pressure has been mounting to reverse the trend. In recent years, South Korean lawmakers have created new incentives to help promote domestic adoption, while quotas have allowed fewer children to leave.

If the decline in global adoptions is to be reversed, says Selman, Africa is likely to lead the way. Ethiopia has emerged in recent years as a top source of orphans available for foreign adoption, though it’s unclear whether other African countries will follow.

“If it’s going to go up, it’ll be from Africa,” he says. “It could be that they set their pace against adoption, and that could have a profound effect.”